Fission gas release from high-burnup mixed-oxide (MOX) fuel pellet with Pu fissile contents of 4.1% during reactivity-initiated accident (RIA) was estimated based on radial Xe concentration profiles in fuel pellet using scanning electron microscopy/electron probe microanalysis (SEM/EPMA) before and after pulse irradiation tests called BZ-3 and BZ-4. The tests were conducted at the Nuclear Safety Research Reactor (NSRR) in Japan Atomic Energy Agency (JAEA). The depression of Xe concentration in the Pu-spot and the crack formation in the peripheral region of fuel pellet were observed after BZ-3 and BZ-4. This kind of cracks was considered to promote the release of the fission gas retained in the Pu-spot. Based on the EPMA results and the effect of the crack formation, the amounts of the release of the gas retained in Pu-spot was estimated to be 0.13 and 0.04 in BZ-3 and BZ-4 tests, respectively. Moreover, taking account of the release of the gas accumulated in the grain boundary in Pu-spot-excluded region and the release of the gas dissolved in the matrix, the total amount of fission gas release was evaluated as 0.33–0.43 and 0.15–0.27 in BZ-3 and BZ-4 tests, respectively. Comparing the results of the fission gas release with the results of rod-puncture test, it was suggested that fission gas release from not only the Pu-spot but also the Pu-spot-excluded region.

使用扫描电子显微镜/电子探针显微分析，基于反应堆引发的事故（RIA）中Pu裂变含量为4.1％的高燃烧混合氧化物（MOX）燃料颗粒的裂变气体释放量，基于燃料颗粒中的径向Xe浓度分布进行估算（ SEM / EPMA）称为BZ-3和BZ-4的脉冲辐射测试前后。这些测试是在日本原子能机构（JAEA）的核安全研究堆（NSRR）上进行的。在BZ-3和BZ-4之后，观察到Pu点Xe浓度的降低和燃料芯块外围区域的裂纹形成。这种裂缝被认为是促进了保留在Pu点中的裂变气体的释放。根据EPMA结果和裂纹形成的影响，保留在Pu点中的气体释放量估计为0。在BZ-3和BZ-4测试中分别为13和0.04。此外，考虑到Pu点排除区域中晶界中累积的气体释放和基质中溶解气体的释放，裂变气体的释放总量分别为0.33-0.43和0.15-0.27分别在BZ-3和BZ-4测试中进行。将裂变气体的释放结果与穿刺试验的结果进行比较，表明裂变气体不仅从Pu点处释放，而且还从Pu点被排除的区域释放。